In silver halide color photographic materials, a color image is formed when the silver halide color photographic material is exposed to light and is subjected to color development wherein an oxidized aromatic primary amine color-developing agent reacts with dye-forming couplers (hereinafter referred to as couplers).
Generally, in this method, the color reproduction is effected by the subtractive color process, wherein in order to reproduce blue, green, and red, respectively yellow, magenta, and cyan color images complementary to them are formed. For the formation of a yellow color image, as a yellow dye-forming coupler (hereinafter referred to as yellow coupler), an acylacetamide coupler and a malondianilide coupler are generally used; for the formation of a magenta color image, as a magenta coupler, for example, a 5-pyrazolone coupler and a pyrazolotriazole coupler are generally used; and for the formation of a cyan color image, as a cyan coupler, a phenol coupler and a naphthol coupler are generally used.
The yellow dye, the magenta dye, and the cyan dye obtained from these couplers are generally formed in silver halide emulsion layers color-sensitive to radiations complementary to radiations which will be absorbed by these dyes or in layers adjacent to said silver halide emulsion layers.
Particularly for the formation of an image, as a yellow coupler, an acylacetamide coupler, represented by a benzoylacetanilide coupler and a pivaloylacetanilide coupler, is generally used. Since generally the former is high in coupling activity with an aromatic primary amine developing agent oxidized product at the time of development, and large in the molecular extinction coefficient of the yellow dye formed therefrom, it is used for photographing color photographic materials that require high sensitivity, particularly color-negative films, and since the latter is excellent in the spectral absorption characteristics and fastness of the yellow dye, it is used for color papers and color reversal films.
However, although benzoylacetanilide-type couplers are high in the coupling reactivity with the oxidized product of an aromatic primary amine developing agent at the time of color development and large in the molecular absorption coefficient of the yellow azomethine dye produced therefrom, they have a defect that the molecular absorption characteristics of the yellow dye are poor, while, although pivaloylacetanilide-type couplers are excellent in the spectral absorption characteristics of the yellow dye, they have defects that the coupling reactivity with the oxidized product of an aromatic primary amine developing agent at the time of color development is low and the molecular extinction coefficient of the yellow azomethine dye produced therefrom is small.
A high coupling reactivity of the coupler and a large molecular extinction coefficient of the dye formed therefrom make possible high sensitivity, a high gamma value, and high color density, thereby bringing about so-called high color-forming properties. The expression "excellent spectral absorption characteristics in yellow color images" means, for example, such absorption characteristics that the spectral absorption decreases sharply at the foot part in the long wavelength side and the undesired absorption of the green region is less.
Therefore, it is desired to develop a yellow coupler having merits of both of them, i.e., high color-forming properties (high in the coupling reactivity of the coupler and large in the molecular extinction coefficient of the dye) and excellent spectral absorption characteristics of the color image.
As the acyl group of acylacetanilide-type couplers, for example, a pivaloyl group, a 7,7-dimethylnorbornane-1-carbonyl group, and a 1-methylcyclohexane-1-carbonyl group are disclosed in U.S. Pat. No. 3,265,506, and a cyclopropane-1-carbonyl group and a cyclohexane-1-carbonyl group are described in JP-A ("JP-A" means unexamined published Japanese patent application) No. 26133/1972. However, these couplers are defective, for example, in that the coupling reactivity is poor, or the molecular extinction coefficient of the dye is small, or the spectral absorption characteristics of the color image are poor.
Concerning the new yellow couplers of the present invention represented by formulas (I-1) and (I-2), the color-forming properties are satisfactory, the molecular extinction coefficient of the dye formed therefrom is high, and the formed dye is good in the decrease of absorbance at the foot part in the long wavelength side, which gives a preferable dye in view of the color reproduction.
In comparison with a conventionally used benzoylacetanilide-type coupler or pivaloylacetanilide-type coupler, the dye produced from the present yellow coupler is remarkably excellent in fastness of the color image under heat and humidity exposure conditions, and it has satisfactory performance in color photographic materials for prints, wherein particularly image stability is required.
However, in the photographic material the dye formed from the present yellow coupler is poor in color image fastness to light, and improvement of the light fastness has been an important problem particularly in consideration of its use in photographic materials for prints.
Concerning the improvement of preservability of color images against light, measures of using light stabilizers, such as hindered phenols and piperidine compounds, are known. European Patent EP Nos. 310,552A1 and EP 393,718A2 describe methods wherein a sulfur-containing cyclic compound is additionally used.
However, the light fastness of the color-formed dye of the present yellow coupler is not satisfactory if the above method is used alone and further improvement is required.
Another problem with the photographic material employing the present coupler is its defect in that the stability of the emulsified dispersion of the coupler is poor. Deterioration of the stability of the emulsified dispersion brings about softening of gradation and a drop of the maximum color density of the color image after color development processing.